The present invention generally pertains to communications systems and methods, and is particularly directed to detection of objects having preferential polarization plane reflection characteristics.
It often is desired to detect the presence of human beings, especially when the humans are within restricted areas. It also is desired to be able to detect other objects, such as guided missiles or aircraft flying parallel to the Earth's surface at relatively low altitudes.
Detection systems based upon the well known Doppler principle are capable of detecting human movement. Doppler systems detect a moving object by sensing a shift in the frequency of microwave energy reflected from the moving object. However, Doppler system also detect blowing rain, snow and sand, waving grass and other moving environmental objects and provides the same type of indications upon detecting such environmental objects as when a moving human is detected.
Conventional radar systems are located in a space satellite or a high-flying aircraft are not capable of detecting guided missiles flying at low altitudes parallel to the Earth's surface because the intensity of microwave energy reflections due to environmental ground clutter is comparable to the intensity of the microwave energy reflections from a missile, whereby such reflections are virtually indistinguishable from each other. One state-of-the art technique for distinguishing missle reflections from ground clutter reflections is to utilize ranging gates, whereby only objects at the range of the missile are detected. However, when the missile flies between hills at a lower altitude than the hilltops, either both the hills and the missile are sensed, or both are masked.